modulator valve (or combination modulator valve) is
damaged and inoperative. As these components are
an integral part of the air brake system, normal brak-
ing may be impaired or inoperative.
During emergency or reduced-traction stops, fully
depress the brake pedal until the vehicle comes to a
safe stop. Do not pump the brake pedal. With the
brake pedal fully depressed, the ABS will control all
wheels to provide steering control and a reduced
braking distance.
Although the ABS improves vehicle control during
emergency braking situations, the driver still has the
responsibility to change driving styles depending on
existing traffic and road conditions. For example, the
ABS cannot prevent an accident if the driver is
speeding or following too closely.
Trailer ABS Compatibility
The Meritor WABCO ABS is designed to communi-
cate with a trailer ABS, if they are compatible. Com-
patibility will result in the illumination of the TRAILER
ABS lamp during vehicle start-up and fault detection.
See
Table 15.1.
The TRAILER ABS lamp will not illuminate unless a
compatible trailer is connected to the tractor. The
dash-mounted lamp will operate as follows when a
compatible trailer is properly connected to the tractor:
•
When the ignition key is turned to the ON posi-
tion, the TRAILER ABS lamp will illuminate mo-
mentarily, then turn off.
•
If the lamp illuminates momentarily during ve-
hicle operation, then shuts off, a fault was de-
tected and corrected.
•
If the lamp illuminates and stays on during ve-
hicle operation, there is a fault with the trailer
ABS. Repair the trailer ABS system immedi-
ately to ensure full antilock braking capability.
IMPORTANT: If a compatible trailer is con-
nected, and the lamp is not illuminating momen-
tarily when the ignition key is turned to the ON
position, it is possible that the lamp is burnt out.
Automatic Traction Control
Vehicles with electronic engines and ABS may have
Automatic Traction Control (ATC). On these vehicles,
the ATC system automatically limits wheel spin dur-
ing reduced-traction situations. In normal braking ap-
plications, the standard air brake system is in effect.
An additional solenoid valve is installed. During
reduced-traction situations, the ATC solenoid valve
controls air pressure to the modulator valves and
they in turn increase, hold, or reduce pressure to the
appropriate brake chambers to provide better traction
whenever wheel spin occurs.
When the ATC system is in the NORMAL mode, it
will apply gentle braking to the spinning wheel, to
feed power to the wheel(s) with better traction. If
both wheels are spinning, the system will signal the
engine to reduce power.
If the system detects wheel spin or a stability event,
the wheel spin/stability telltale illuminates and an
alert is shown on the driver display. See
Table 15.1.
Pressing the ATC SPIN switch (
Fig. 15.3) shuts ATC
off and allows drive wheel spin. An alert is shown on
the driver display. Pressing the switch again, or cy-
cling the ignition key, will cycle the system back to
normal operation.
NOTICE
The ATC spin feature is intended to be used
under specific slippery conditions that require
momentary increased wheel spin. Using this op-
tion for an extended period of time may damage
the vehicle brake system.
After the ignition switch is turned on, the TRACTOR
ABS lamp comes on for about three seconds. After
three seconds, the warning light goes out if all of the
tractor’s ABS components are working.
IMPORTANT: If the ABS warning light does not
work as described above, or comes on while
driving, repair the ABS immediately to ensure
full antilock braking capability.
f611333
03/02/2016
ATC
SPIN
Fig. 15.3, ATC SPIN Switch
Brake Systems
15.5
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